175. Hence in the following cases, even though there be serious matter, a sin is not mortal, on account of lack of full advertence. (a) When without one’s will there is no full advertence to the act itself, as happens with those who are half-asleep, or who are under the influence of drugs, or who are mentally confined by anxiety or physical pain, etc. (see on Human Acts, 24 sqq.). (b) A sin is not mortal when there is no full advertence to the sinfulness or to the gravity of the act. Those who through no fault of their own are unaware that an act is sinful, or that it is a mortal sin (e.g., children, the half-witted, or the uninstructed), have no full advertence to the malice of the act; likewise, those who, without being responsible for their inadvertence, do not think at the moment of the sinfulness or seriousness of what they do (e.g., those who think out plans for revenge before they have taken second thought on its immorality).
176. Signs that indicate that there was no full advertence are: (a) if afterwards one can scarcely recall what happened; (b) if shortly afterwards one cannot be sure what was one’s state of mind at the time.
177. Though full advertence is required for a mortal sin, it is not required that this advertence be the most perfect. (a) It is not necessary that the advertence be preceded by long deliberation, for advertence can be full even when the consideration is only momentary, (b) It is not necessary that advertence be continued during the commission of a sin, for what follows is foreseen if adverted to at the beginning. (c) It is not necessary that advertence to the malice of the sin be clear or exact. One who perceives that there is some special malice in robbing a church, even though he does not understand just what the malice is, has sufficient advertence to become guilty of sacrilege. Likewise, one who has doubts as to whether a certain sin is mortal, or who suspects that it is mortal, has sufficient advertence for grave guilt if he commits that sin. (d) It is not necessary that advertence to the malice of the sin be reflex (i.e., that one advert to the fact that one is conscious of the gravity of the sin); for to will the malice, it suffices that one be conscious of the malice. (e) It is not necessary that advertence to the malice of the sin be explicit (i.e., that one have in mind the precise nature of sin as an offense against God, which produces a stain on the soul and incurs the debt of punishment); for to will evil and its gravity, it suffices that one perceive the evil and its gravity, even though one does not analyze the meaning or seek out the ultimate reasons.
178. The third condition required that a sin be mortal is that full consent of the will be given it, for no one separates him self from God except through his own free choice. (a) Consent is not full, when there has not been full advertence, or when an act has been done under violent compulsion; (b) consent is full when there has been full advertence and no forceful compulsion (see above on Violence, 52).
179. Indications that consent was not full are: (a) if before the sin the person was of tender conscience and had habitually a horror of grave sin; (b) if at the time of the sin the person recoiled from the sinful suggestion—e.g., if he had a hatred for it as soon as it was fully perceived, or if he was saddened at the temptation, or if he kept from an external act that could have been easily performed; (c) if after the sin the person was conscientious, and yet had doubts as to whether consent was given.
180. Venial Sin.—A sin is venial, or more easily pardonable, when by it one turns inordinately towards some created good, not so, however, as to forsake God as one’s Last End or to prefer self-will to the divine friendship.
181. The first condition required that a sin be called venial is that its matter be light, either in reality, or in the invincible belief of him who commits it. The criteria by which we may know what matter is light are authority and right reason (see above, 171).
182. The matter of a sin is light in two ways. (a) From the character of the act, the matter is light when the good which is injured is finite and of minor importance. Thus, truth about trivial things is of less importance among finite goods, and consequently a small lie about some unimportant matter, which helps and does not harm the neighbor, is light matter. (b) From the quantity of the matter, the matter is light when the good injured is of major importance but divisible. An example here is a theft that works only small harm (see above, 172).
183. The second condition for a venial sin is that there be some advertence to the malice of the act. (a) The advertence is not full when the matter is grave, and the act done without compulsion, for else the sin would not be venial but mortal. (b) The advertence may be full or partial when the matter is light.
184. The third condition for a venial sin is that there be some consent of the will to the malice of the act. (a) The consent is not full when the matter is grave, for else the sin would be mortal. (b) The consent may be either full or partial when the matter is light.